Design of hole transport type host for stable operation in blue organic light-emitting diodes

Molecular design of the hole transport type host for mixed host was investigated to improve the lifetime of the phosphorescent organic light-emitting diodes. A negative polaron stabilizing hole transport type host design was employed and the effect of the negative polaron stabilizing unit was investigated. Dibenzofuran or benzonitrile was introduced as the negative polaron stabilizing unit in the bicarbazole backbone structure of the hole transport type host. Two host materials were synthesized and the comparison of them proposed that the negative polaron stabilizing unit is a key to the lifetime of the phosphorescent organic light-emitting diodes. The dibenzofuran and benzonitrile embedded bicarbazole hosts performed better than the mCBP host. The dibenzofuran and benzonitrile modified bicarbazole hosts demonstrated high external quantum efficiency of 18.6 and 19.1%, respectively and lifetime extension by 30% compared with the conventional host without the negative polaron stabilizing unit.